1,721,004 research outputs found
Correlated one-hole spectra of YBa2Cu3O7 in the bulk and at the surface
No full textThe one-hole valence spectrum of YBa2Cu3O7 is calculated using an accurate tight-binding hamiltonian and a Hubbard model to treat correlation effects. Intra-atomic Coulomb integrals for holes sitting on Cu or O sites are considered and the one-hole self-energy is computed in the low density approximation. The calculated spectrum is compared with photoemission and X-ray emission experiments. This allows to point out a number of problems that arise in assigning the observed structures to a specific atom and to understand some aspects of the data. To evaluate the role of the surface in determining the shape of the photoemission energy distribution curves, the one-hole spectrum is calculated for the Ba-O4 surface. Oxygen induced surface states are shown to be important in determining the intensity of the observed structures. © 1989 Springer-Verlag
Hole density and Tc behaviour in YBa2Cu3O7 - x
No full textThe behaviour of the hole number in YBCO systems as a function of the oxygen deficiency x is studied theoretically by calculating the density of electron states for several different superstructures formed by periodic arrangements of the oxygen vacancies. The characteristic features of the electronic properties for chain copper sites with different coordination are pointed out and their relevance in determining the number of carriers for oxygen planes is illustrated. It is shown that the curve of the hole number as a function of x shows plateaus and jumps similar to those found in the Tc versus x curves if the de-oxygenation process takes place by forming fragmented chains. Structures formed by filled and empty chains only give a smooth hole behaviour as a function of the composition. The results of the numerical calculations can be understood by a simple model giving the Fermi energy shift in terms of the concentrations of Cu(1) sites with different coordination. © 1990
L’INDIVIDUAZIONE DELLO STREPTOCOCCO MUTANS, DEI LATTOBACILLI E DELLA CANDIDA ALBICANS PER LA PREVENZIONE PRIMARIA DELLA PATOLOGIA CARIOSA
No full textLAVORO PER ESTESO su ATTI CONGRESSUAL
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
PARODONTOPATIA DA DEPOSITO ABNORME DI TARTARO IN ETA' PEDIATRICA: DESCRIZIONE DI UN CASO CLINICO
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